A wonderful part of working in audio is all the technical terms and diagrams. No matter how much I think I know, there is always something new that makes me scratch my head.
One of the early head-scratchers, for me, was the microphone polar chart. I grew up knowing charts as having an X, Y, and sometimes Z baseline. Pie charts, well those are pretty easy to understand. I really shouldn’t talk about pie charts when I’m hungry. Yummmmmmmm.
Enough food talk and back to the polar chart. Upon seeing it, I was introduced to a flat looking chart that represented something on a 3-dimensional level. So, like any good sound guy, I started reading all about polar charts and how they are used.
The key to understanding polar charts is understand two terms; on-axis and off-axis.
If I point a gun at you and you are looking down the barrel, then you are on-axis to the gun. Therefore, if I point a microphone directly at you, you are on-axis with the microphone. Anything that is not on-axis is off-axis.
Microphones have unique polar patterns. Polar patterns describe how much sound they can pick up depending on the degree in which the sound is on or off axis. For example, if you point a cardioid microphone away from yourself 180-degrees, the microphone won’t pick up any of your voice.
Let’s now pick apart a polar chart.
The top of the circle indicates “on-axis” or 0-degrees. From there, moving clockwise or counter-clockwise, you have increasing degrees until you reach the bottom which is 180-degrees. This is a 3D chart so think of the circle more like a perfectly round ball with the microphone in the middle pointing up.
Looking at the polar patterns on the above link, you see that a Hypercardioid pattern is different from a cardioid primarily in that the Hypercardioid can detect sound behind the microphone. Also, the cardioid has a wider range left to right. Knowing your needs, you pick microphones with the best polar patterns for the job.
Polar pattern charts can take on an additional level of complexity. They can show the varying response of the microphone based on the frequencies that are detected. For example, this polar pattern chart shows the response at 125, 500, and 1000 Hz for the Shure SM58. In this case, the chart is upside down so the 0-degree is at the bottom instead of the top.
Providing the best house sound is more than setting gain structure and mixing. You should know your equipment and know when the appropriate equipment, like the right type of microphone, should be used. Polar patterns and charts aren’t just techie talk for the sake of being geeky. They are microphone properties that tell you how the microphone can be used.